The Trinity is a doctrine that we cannot fully understand, although there is much we can say. But we need not fully understand it in order to affirm it. It is taught in God’s Word, and we are responsible to believe what God’s Word teaches even when complete comprehension escapes us.
All drivers obey the law of noncontradiction. No one pulls out into the path of a speeding eighteen-wheeler thinking that the truck is both going to hit them and not hit them at the same time. When someone claims that contradiction and truth are compatible, show them that they obey the law of noncontradiction everyday without thinking about it.